Storage tube with target having conductive surface exposed through random cracks in dielectric coating

ABSTRACT

A target for use in an electronic tube is provided on a conductive layer of a support member and it comprises solid dielectric domains adhered to the conductive layer and spaced from one another. The peripheries of the dielectric domains have a random configuration so that the spacing therebetween defines random cracks exposing areas of the conductive layer. The target can also be a metallic mesh having openings of non-regular cell size if the metallic mesh is provided with dielectric thereon which has random cracks therein which exposes areas of the metal.

United States Patent [191 Soltys Mar. 19, 1974 STORAGE TUBE WITH TARGET HAVING CONDUCTIVE SURFACE EXPOSED THROUGH RANDOM CRACKS IN DIELECTRIC COATING [75] Inventor: Michael N. Soltys, Hillsboro, Oreg. [73] Assignee: Tektronix, Inc., Beaverton, Oreg. [22] Filed: Aug. 3, 1972 [21] Appl. No.: 277,556

[52] US. Cl. 313/68 R, 313/68 A, 313/92 R. 313/329, 313/349 [51] Int. Cl H01j 29/30, HOlj 29/41 [58] Field of Search 313/68 R, 68 A, 89, 92 R."

[56] References Cited UNITED STATES PATENTS. 2.726.328 12/1955 Clogston 313/68 R X Gibson. Jr 313/68 A Hutchins et al 313/68 R X Primary ExaminerI-Ierman Karl Saalbach Assistant Examiner-Siegfried H. Grimm [57] ABSTRACT A target for use in an electronic tube is provided on a conductive layer of a support member and it comprises solid dielectric domains adhered to the conductive layer and spaced from one another. The peripheries of the dielectric domains have a random configuration so that the spacing therebetween defines random cracks exposing areas of the conductive layer. The target can also be a metallic mesh having openings of non-regular cell size if the metallic mesh is provided with dielectric thereon which has random cracks therein-which exposes areas of the metal.

14 Claims, 11 Drawing Figures mm PATENTED 1914 SHEET 1 BF 2 3,798,477

WRITE R.EAD WRITE lisw WRITE READ 42 WALL-Egg- BACKGROUND OFTHE INVENTION The present invention is related to electron image storage apparatus, and more particularly to a storage target for a cathode ray tube which stores an electron image formed on such target for a controllable time and produces a light image and/or electrical signals corresponding to such electron image. The storage target includes a layer of conducting material coated on one surface of a support member of insulating material, and a storage dielectric material adhered onto the conducting material which has random cracks therein defining dielectric domains having random peripheries with the cracks exposing areas of the conducting material.

The storage target can take the form of a regular or random patterned metal mesh or mesh having conductive characteristics on which dielectric has been adhered with the dielectric having random cracks therein forming dielectric domains thereby exposing areas of the mesh.

The dielectric material may be made of phosphor material if direct viewing is desired and the separation of the dielectric domains, since it provides pathways for electron movement, enables them to store a bistable charge image formed thereon for an indefinite but controllable time as well as emitting a light image corresponding to such charge image.

The support member is made of transparent material when the conductive layer and random cracked pattern of dielectric are carried thereby.

The present invention also includes a free-standing metal mesh having openings of random configuration which can be used as a collector mesh in an electron tube. The present invention further includes methods of manufacture of storage targets and metal mesh employing random configuration such as described above.

A storage target made in accordance with the present invention is especially useful when employed in a bistable direct-viewing type of storage cathode ray tube which forms part of a cathode ray oscilloscope to store the wave forms of transient electrical input signals for extended examination. Such a tube, however, can also be for any conventional storage tube operation such as, for example, in radar or sonar equipment or electronic computers.

The present invention is an improvement of the storage target of US. Pat. No. 3,293,474 which discloses a metal mesh of uniform or coherent configuration coated on a transparent support member and dielectric areas separated by the areas of the mesh. It is very costly to produce this target structure due to use of sophisticated production equipment and optics. Moire interaction can also occur in using this target structure of uniform configuration. In a storage target of uniform configuration, a part of a waveform extending along adjacent domains of the target will present a discernible stepped configuration there'along constituting distortion of this part of the waveform. Edge resolution and contrast of the displayed information will lack sharpness.

The present invention overcomes the drawbacks of the target structure of US. Pat. No. 3,293,474 by the making of a storage target that is economical. It will not present any moire patterns since it does not have a regular pattern, the information displayed on the target will have less distortion and the resolution and contrast of the displayed information will have a sharp delineation. 7

An object of the present invention is to provide an improved apparatus for storing electron images.

Another object of the present invention is the provision of an improved storage target for storing an electron charge image thereon.

A further object of the present invention is to provide an electron storage target that has conductive means on which is disposed a suitable dielectric having random cracks therein exposing areas of the conductive means.

An additional object of the present invention is the provision of an electron storage target wherein the conductive. means is a continuous layer on a rigid support means over which random domains of dielectric material are disposed thereby enabling a storage tube of large size to be produced since the target is rugged and reliable.

A still further object of the present invention is to provide an electron storage target wherein the conductive means is a metallic mesh having randomsized openings therein and the metallic sections have disposed thereon dielectric material which has random cracks therein exposing areas of the metal sections.

Still an additional object of the present invention is the provision of an electron storage target wherein the conductive means is a metallic mesh having openings of the same size, and the metallic sections have disposed thereon dielectric material which has random cracks therein exposing areas of the metallic sections.

Still another object of the present invention is to provide a free-standing metallic mesh having random-sized openings therein.

Still a further object of the present invention is the provision of methods of manufacture of the storage targets and metallic mesh.

Other objects and advantages of the present invention will be apparent from the following detailed description of preferred embodiments thereof and from attached drawings of which:

FIG. 1 is a diagrammatic view of a storage tube in accordance with the present invention;

FIG. 2 is a part horizontal view taken along line 2 2 of FIG. 1 showing at an enlarged scale one embodiment of a storage target in accordance with the present invention;

FIG. 3 is a view taken along the line 3 3 of FIG. 2 showing a part of the rear section of the storage target;

FIG. 4 is a cross-sectional view of a tank for the electrophoretic deposition of dielectric material onto a conductive layer;

FIG. 5 is a cross-sectional .view of a storage target after the dielectric layer has been deposited on the conductive layer;

FIG. 6 is a part cross-sectional view at an enlarged scale showing the configuration of the dried domains of dielectric material;

FIG. 8 is similar to FIG. 7 but with the metallic v coated dielectric removed and photographic film in place thereof;

FIG. 9 is an enlarged section of a metallic mesh having randomsize openings therein;

FIG. 10 is a view similar to FIG. 9 having dielectric on mesh which is provided with random cracks therein; and

FIG. 11 is an enlarged section of a regular pattern mesh having dielectric thereon which is provided with random cracks therein.

A direct-viewing bistable storage tube 10 having a storage target 12 made in accordance with the present invention is shown in FIG. 1. This storage tube may have a single electron gun including a cathode 14, a control grid 16, a focusing anode structure 18 in addition to a pair of horizontal deflection plates 20 and a pair of vertical deflection plates 22. The single electron gun may be employed to produce either a writing beam or a reading beam of electrons by changing ganged switches 24, 26 and 28, which are connected respectively to control grid 16, horizontal deflection plates 20 and vertical deflection plates 22, between WRITE and READ positions in accordance with conventional storage tube operation as described in the abovementioned patent. Separate writing and reading electron guns can, of course, be employed.

The writing beam forms an electron charge image on storage target 12 by deflection of the writing beam across such storage target in accordance with an input signal applied to the vertical deflection plates 22. The reading beam is employed to scan the storage target 12 thereby resulting in an electrical readout signal on lead 30 corresponding to the charge image stored on the storage target. The scanning operation can be in accordance with a conventional television raster pattern.

One or more flood guns 32 may be provided within the envelope of storage tube 10 in order to bombard storage target 12 in a substantially uniform manner with low velocity flood electrons in order to maintain or hold the charge image produced on the storage target by the writing beamafter the writing beam no longer bombards the target.

Storage target 12 includes a thin coating 34 of light transparent conductive material, which is preferably tin oxide, and storage dielectric layer 36 in the form of domains having a random peripheral configuration separated by randomly-formed cracks 38 which expose areas of metallic-coating or film 34. Metallic film 34 is deposited on transparent face plate 40. The dielectric portion of storage target 12 has the appearance of a mudflat when viewed from the direction of the cathode. When the target voltage applied to conductive film 34 is within the stable range of target voltages over which the dielectric layer 36 of the storage target will store a charge image for an indefinite controllable time, the writing beam of high velocity electrons produces by secondary emission a charge image on dielectric layer 36 which is more positive than the areas not struck by the beam. The potential of the written charge image is above a critical voltage corresponding to the first crossover point on the secondary emission curve of the dielectric, while the remaining unwritten areas of dielectric layer 36 have a potential below this critical voltage. The flood electrons impinging on the storage target produce substantial secondary electron emission from the target to drive the potential of the written areas of dielectric layer 36 to a voltage stable state corresponding to the voltage of conductive film 34, and the flood electrons drive the potential of the unwritten areas to a low voltage stable state corresponding to the voltage applied to the cathode of flood guns 32. Reference is made to U. S. Pat. No. 3,293,473 for a complete description of the operation of a bistable storage tube. Utilization of the information stored by storage tube 10 as well as erasure thereof is completely disclosed in this patent.

The dielectric'layer 36 of the storage target 12 may be made of phosphor material including conventional phosphors, such as P-l type phosphor, and photoconductive phosphors, so that the dielectric layer produces a light image corresponding to the charge image stored thereon when the storage tube is of a directviewing type. In this case, the information stored on the storage target can be viewed directly prior to reading out the stored information. A collimating-electrode 42 may be provided as a wall coating on the interior surface of the funnel portion of tube 10 adjacent storage target 10 and it is connected to a positive DC voltage to focus the flood electrons onto the storage target and to prevent distortion of the stored image because the positive target areas attract some of the electrons away from the adjacent negative areas.

If the dielectric layer 36 is not of phosphor but is of another secondary emissive material, the storage tube must be provided with a conventional readout circuit to produce an electrical readout signal corresponding to the charge image stored on the storage target. Such readout operation can be accomplished in accordance with that disclosed in the aforementioned U. S. Pat. No. 3,293,474 and need not be discussed in greater detail.

As shown in FIGS. 2 and 3, one embodiment of the storage target 12 of the present invention includes thin metallic coating 34 deposited on one surface of transparent support plate 40, which is preferably glass and is a face plate section of a cathode ray tube envelope. Support plate 40 provides a mounting means for target 12. The envelope preferably includes funnel section 44 of ceramic material which is sealed to the glass face plate 40 via a glass frit seal 46. The metallic coating 34 is formed of light opaque conductive material such as aluminum or silver, or a light transparent conductive material such as tin oxide, and it provides a collector electrode. A section 34a of collector electrode 34 extends through seal 46 to the exterior of the envelope in order to provide an electrical lead portion for connecting collector electrode 34 to an electrical source.

Dielectric layer 36 is composed of independent dielectric domains with each of the domains having a random configuration, i.e. the peripheries are of random configuration so that cracks 38 are provided between adjacent dielectric domains thereby exposing random areas of collector electrode 34. The randomly-formed dielectric domains are separated from each other by the random cracks. The randomly-spaced dielectric domains are in intimate contact with the collector electrode 34, however, the dielectric layer 36 does not form a continuous layer thereover so that the capacitance formed by such randomly-spaced dielectric domains, when charged by the writing beam impining on the storage target, is substantially reduced. The randomly-spaced dielectric domains are of substantially the same thickness.

A graticle scale 48 in the form of a plurality of scribed lines may be provided on the inner surface of face plate 40 beneath storage target 12 when the dielectric layer is of phosphor in order to provide an internal graticle for examining the light image produced on the storage target. The internal scale 48 may be provided by deposits of glass frit printed on the inner surface of glass plate 40 to provide the graticle lines. The internal graticle may be edge-lighted by projecting light through the surrounding edge of face plate 40.

The preferred method for making targets having dielectric domainsor areas of random configuration on conductive means with the random cracks between the dielectric domains exposing sections of the conductive means is in accordance with the electrophoretic technique. FIGS. 4 6 illustrate the making of a faceplate target structure. A faceplate or dielectric support 40 has one surface coated with metallic film 34 and is mounted on a metal frame 50 which is in electrical engagement with metallic film 34 and which is connected to a negative terminal of a 120V to 240V of a constant current DC source of supply. A counterpoise electrode 52 is spaced from frame 50 about 4 cm. and it is connected to the positive terminal of the DC voltage. Counterpoise electrode 52 establishes a uniform electric field between frame 50, metallic film 34 and electrode 52 to provide electrophoretic action.

Support 40, frame 50 and electrode 52 are disposed in a suspension of colloidal dielectric material, isopropanol with 2 percent of water and a trace of trivalent cation such as aluminum nitrate thereby providing a colloidalsuspension in container C. Upon an electric field being established when the DC voltage is applied to frame 50, film 34 and electrode 52 within the colloidal suspension, dielectric particles will be attracted to and plated onto frame 50 and film 34 in accordance with electrophoresis thereby providing a continuous dielectric coating of dielectric material when support 40 is removed from the plating bath as shown in FIG. 5. Dielectric materials such as aluminum oxide or magnesium oxide, and silicate phosphors such as P-l phosphor commonly known as zinc orthosilicate or the like, can be used to form the colloidal suspension.

The plating time to provide a desired dielectric coating of 5 microns thickness will be about 10 minutes. The target structure after being removed from container C is dried in ambient air in a vertical position to preclude formation of water marks for about 5 minutes whereby random cracks '38 are formed in the dielectric layer thereby forming separate dielectric domains having arcuate-shaped configurations in cross section as shown in FIG. 6. Cracks 38 extend to conductive film 34 and expose areas of film 34. This target having the randomly-formed dielectric domains and cracks, which resembles a mudflat, is now ready for assembly onto a CRT envelope via frit seal 46 and it can now operate as a bistable target. The manufacture of target 12 is, therefore, very economical having the advantages of high resolution, capability of field-fo'rmingor of supporting dielectric structures for storage purposes, large targets may be made, and having no moire interaction with other structures, whether random or periodic.

A metallic mesh electrode having openings of random configuration instead of conventional metallic mesh electrodes having openings of regular polygonal configuration can be realized in accordance with the present invention.

A target structure made in accordance with the steps set forth hereinabove to make target 12, i.e. place support 40 with film 34 thereon in colloidal bath, electrophoretic deposition for about 10 minutes and remove target structure from bath and allow to dry for five minutes. Magnesium oxide or aluminum oxide is the preferable dielectric to be used for making a mesh electrode. The dried mudflat target is then placed in a Bell jar under a 10' Torr vacuum and a deposit of 1000-2000 angstrom layer of chrome metal 54 is applied onto target 12 as shown in FIG. 7 so that chrome metal 54 is deposited as a layer onto dielectric domains 36 and onto conductive film 34 where cracks 38 occur. The chrome-coated target is removed from the Bell jar and the chrome-coated dielectric domains 36 are removed from metal film 34. If the dielectric is magnesium oxide, acetic acid solution is used to remove the dielectric particles, and, in the case that aluminum oxide dielectric is used, it is removed by a mild solution of sodium hydroxide or potassium hydroxide.

A high resolution photographic film 56 is placed onto the random pattern of chrome metal 54 and the film 56 is exposed via light through faceplate 40 and the tin oxide film 34 to form a photographic pattern dictated by the random pattern of the chrome metals and the unexposed random pattern where the dielectric domains were located. Film 56 is thereafter developed and it is placed on an electro-forming mandrel having pq ii JELhQLQIQL HEEQ E. th AZ:. 1 1 is manufactured by Azoplate Corp., Murray Hill, N. J. This is exposed to light and processed in accordance with conventional practice to remove the exposed areas leaving the crack pattern as voids in the photoresist.

Nickel is plated in accordance with conventional plating practices into the void areas on the electroforming mandrel thereby forming a nickel mesh having randomly-formed openings. The nickel mesh is removed from the mandrel via acetone which dissolves the photoresist and frees the mesh therefrom.

The free mesh is placed in a Bell jar and chrome coating of about 1000 angstroms is thermally vapor deposited onto both sides of the mesh to enable the mesh to be properly fritted into position in a CRT. A section of such a mesh 58 so formed is shown in FIG. 9 and it can be effectively used as a control grid in a CRT or as a mesh in a transmission CRT.

Mesh 58 can have applied thereto a thin coating of dielectric 36 in the same manner as taught in conjunction with making target structure 12 in FIGS. 4 6, whereupon cracks 38 formed in the dielectric upon drying of the dielectric will expose metallic areas of mesh 58 where the cracks 38 occur as shown in FIG. 10 thereby providing a bistable storage target having randomly-shaped openings therethrough for use in a transmission or charge transfer CRT.

A metal mesh 60 of FIG. 11, which has openings of the same size defining a repetitive configuration, can be coated with a thin coating of dielectric in the same manner as the random mesh 58 of FIG. 10 and a coherent mesh with random cracks 38 therein exposing areas of the metal of the mesh where the cracks occur can be so formed and utilized as a bistable target in a transmission or charge transfer CRT. As can be discerned from FIG. 11, the dielectric 36 will have a cross-shaped configuration where the wires of the mesh intersect with dielectric sections on the wires between adjacent legs of the cross which are spaced therefrom providing the cracks 38 and exposing the bare wire therebetween. The mesh targets of FIGS. 10 and 11 are mounted for example on rigid mounting members which are in turn mounted within the funnel portion of tube 10. The mesh structures of FIGS. 9 11 after being mounted in position in the funnel are preferably electrically connected exteriorly via the connector structure disclosed in U. S. Pat. No. 3,665,239.

It will be obvious to those having ordinary skill in the art that many changes may be made in the details of the above-described preferred embodiments of the present invention without departing from the spirit thereof. The scope of the present invention should therefore only be determined by the following claims.

The invention is claimed in accordance with the following:

l. A storage target for storing an electron image comprising:

a member of conductive material; and a coating of dielectric material deposited over said member by application of a slurry containing the dielectric material onto said member and drying said slurry so that random cracks are formed in said coating with said random cracks extending through said coating and exposing conductive areas of said member corresponding to said random cracks.

2. A storage target according to claim 1 wherein support means of nonconducting material is providedon which said member of conductive material is disposed.

3. A storage target according to claim 2 wherein said member of conductive material is a continuous layer on said support means.

4. A storage target according to claim 1 wherein said member of conductive material is a mesh having random-sized openings.

5. A storage target according to claim 1 wherein said member of conductive material is a mesh having the same-size openings.

6. An electron storage tube comprising:

an evacuated envelope;

a storage target within said envelope including conductive means and coating means of dielectric material deposited over said conductive means by application of a slurry containing the dielectric material onto said conductive means and drying said slurry so that random cracks are formed in said coating with said random cracks extending through said coating and exposing conductive areas of said conductive means corresponding to said random cracks; means mounting said storage targetin position in said envelope;

means electrically connecting said conductive means to the exterior of said envelope;

writing means disposed within said envelope for providing a writing beam of high velocity electrons for impinging said storage target and for deflecting said writing beam across said storage target to produce an electron image on said dielectric material; and

holding means disposed within said envelope for providing low velocity electrons substantially uniformly over said storage target thereby causing said electron image to be stored thereon for a time on said dielectric material.

7. An electron storage tube according to claim 6 wherein said mounting means comprises a light transparent glass face plate forming part of said envelope on which said storage target is mounted and said dielectric material is phosphor material.

8. An electron storage tube according to claim 6 wherein reading means is disposed in said envelope for scanning said storage target with a reading beam of electrons thereby producing an electrical readout signal on said conductive means corresponding to said electron image stored on said dielectric layer.

9. An electron storage tube according to claim 6 wherein said storage target is a bistable storage target so that said electron image can be stored thereon for an indefinite controllable time.

10. An electron storage tube according to claim 6 wherein said conductive means comprises a continuous film disposed on said mounting means.

11. An electron storage tube according to claim 6 wherein said conductive means comprises mesh means having random-size openings. 7

12. An electron storage tube according to claim 6 wherein said conductive means comprise mesh means having regular-size openings.

13. A direct-viewing storage target for storing an electron image and producing a light image corresponding to such electron image comprising:

a light-transparent support member of electrical insulative material;

a layer of conductive material disposed on one surface of said support member in the form of a continuous layer; and

a storage dielectric coating of secondary emissive phosphor material deposited over said continuous conductive layer by application of a slurry containing the phosphor material onto said continuous conductive layer and drying said slurry so that random cracks are formed in said coating with said random cracks extending through said coating and exposing conductive areas of said continuous conductive layer corresponding to said random cracks.

openings therethrough. 

1. A storage target for storing an electron image comprising: a member of conductive material; and a coating of dielectric material deposited over said member by application of a slurry containing the dielectric material onto said member and drying said slurry so that random cracks are formed in said coating with said random cracks extending through said coating and exposing conductive areas of said member corresponding to said random cracks.
 2. A storage target according to claim 1 wherein support means of nonconducting material is provided on which said member of conductive material is disposed.
 3. A storage target according to claim 2 wherein said member of conductive material is a continuous layer on said support means.
 4. A storage target according to claim 1 wherein said member of conductive material is a mesh having random-sized openings.
 5. A storage target according to claim 1 wherein said member of conductive material is a mesh having the same-size openings.
 6. An electron storage tube comprising: an evacuated envelope; a storage target within said envelope including conductive means and coating means of dielectric material deposited over said conductive means by application of a slurry containing the dielectric material onto said conductive means and drying said slurry so that random cracks are formed in said coating with said random cracks extending through said coating and exposing conductive areas of said conductive means corresponding to said random cracks; means mounting said storage target in position in said envelope; means electrically connecting said conductive means to the exterior of said envelope; writing means disposed within said envelope for providing a writing beam of high velocity electrons for impinging said storage target and for deflecting said writing beam across said storage target to produce an electron image on said dielectric material; and holding means disposed within said envelope for providing low velocity electrons substantially uniformly over said storage target thereby causing said electron image to be stored thereon for a time on said dielectric material.
 7. An electron storage tube according to claim 6 wherein said mounting means comprises a light transparent glass face plate forming part of said envelope on which said storage target is mounted and said dielectric material is phosphor material.
 8. An electron storage tube according to claim 6 wherein reading means is disposed in said envelope for scanning said storage target with a reading beam of electrons thereby producing an electrical readout signal on said conductive means corresponding to said electron image stored on said dielectric layer.
 9. An electron storage tube according to claim 6 wherein said storage target is a bistable storage target so that said electron image can be stored thereon for an indefinite controllable time.
 10. An electron storage tube according to claim 6 wherein said conductive means comprises a continuous film disposed on said mounting means.
 11. An electron storage tube according to claim 6 wherein said conductive means comprises mesh means having random-size openings.
 12. An electron storage tube according to claim 6 wherein said conductive means comprise mesh means having regular-size openings.
 13. A direct-viewing storage target for storing an electron image and producing a light image corresponding to such electron image comprising: a light-transparent support member of electrical insulative material; a layer of conductive material disposed on one surface of said support member in the form of a continuous layer; and a storage dielectric coating of secondary emissive phosphor material deposited over said continuous conductive layer by application of a slurry containing the phosphor material onto said continuous conductive layer and drying said slurry so that random cracks are formed in said coating with said random cracks extending through said coating and exposing conductive areas of said continuous conductive layer corresponding to said random cracks.
 14. A mesh for use as an electrode in an electron discharge means comprising a planar member having electrically-conductive surfaces and random-shaped openings therethrough. 